The present invention is directed to systems and devices for converting wind energy into electrical power, and more particularly to governing mechanisms to provide overspeed protection and power regulation for such systems and devices, and also to features for improving the efficiency and wind tracking and power regulation capability of these systems and devices.
Wind energy conversion systems continue to gain favor as lower cost and more environmentally sound alternatives to more centralized methods of generating electricity. Devices and systems for converting wind energy frequently are used to supplement the electric power available over power transmission lines, and may be the sole source of electric power in remote areas where electrical power transmission is impractical or impossible. In addition to generating electrical power, wind conversion devices also are used to provide direct mechanical power via gear trains and other mechanisms driveably coupled to a wind-driven rotor or shaft.
All of these devices are subject to variations in wind velocity. Usually it is advantageous to design a system with a propeller capable of delivering useful amounts of electrical power at relatively low wind velocities. However, given that the force due to wind increases in proportion to the cube of the wind speed, high wind speeds even if only occasional or momentary can damage system components.
Accordingly, wind energy conversion devices advantageously incorporate governing mechanisms to prevent propeller assemblies from rotating at unduly high speeds in response to high winds. These include whole blade pitching mechanisms, airfoil spoilers or flaps, blade tip breaks and ailerons. Other governing mechanisms act upon the entire propeller rather than the individual propeller blades, to tilt the propeller plane out of the direct wind path. U.S. Pat. No. 5,746,576 (Bayly) discloses a particularly effective governing mechanism of this type, in which a propeller structure is supported to rotate on a vertical yaw axis, and also to pivot on a governing axis inclined about 30 degrees from the vertical, such that the propeller structure is biased by gravity into a normal operating position in which the propeller plane is perpendicular to the wind. Wind of a sufficient speed overcomes gravity, to incline the propeller plane relative to the wind direction by an angle that varies in proportion to the wind velocity, for the desired governing action.
In larger capacity wind energy conversion devices, there is greater need to limit forces acting upon the components supporting the propeller. This increases the need for governing mechanisms operable upon individual propeller blades, avoiding the need to tilt the entire propeller structure including the blades and propeller shaft. Larger propellers also give rise to concerns with blade fabrication. Traditional fiberglass propeller blades require considerable labor in finishing and smoothing the blades. Cost reductions are possible if the blades are formed by injection molding. However, standard injection molding machinery is not well suited for fabricating larger propeller blades. Potential cost savings are diminished or lost, due to the need to provide special configurations or equipment for molding larger blades. Further, larger propeller blades formed by injection molding are subject to irregularities from uneven cooling along the blade length due to different thicknesses and contours.
Conventional systems raise several more concerns not specifically tied to propeller blade size, such as the need for increased efficiency, quieter operation, lower manufacturing cost, and more predictable blade behavior over a range of wind velocities triggering governing action.